1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device.
In this specification, a semiconductor device generally means a device which can function by utilizing semiconductor characteristics, and an electrooptic device, a semiconductor circuit, and electronic equipment are all semiconductor devices.
2. Description of the Related Art
Attention has been focused on a technique for forming a transistor using a semiconductor thin film formed over a substrate having an insulating surface. The transistor is applied to a wide range of electronic devices such as an integrated circuit (IC) and an image display device (also simply referred to as display device). A silicon-based semiconductor material is widely known as a material of the semiconductor thin film applicable to the transistor. As another material, an oxide semiconductor has been attracting attention.
For example, a transistor including a semiconductor layer formed of an amorphous oxide including indium (In), gallium (Ga), and zinc (Zn) (an In—Ga—Zn—O-based amorphous oxide) is disclosed (see Patent Document 1). Further, titanium, tungsten, molybdenum, or the like is used for a source electrode layer and a drain electrode layer which are provided to be in contact with such an oxide semiconductor film (see Patent Documents 2 and 3).